6. Project Summary/Abstract The long-term goal of this study is to understand the molecular mechanisms that control motile cilia assembly and function. Motile cilia play essential roles in multiple physiological processes including mucociliary clearance in the respiratory system, cerebrospinal fluid (CSF) circulation and sperm motility. Dysfunction of motile cilia and flagella underlies the human syndrome of primary ciliary dyskinesia (PCD). While the ultrastructure of motile cilia is well characterized, many important aspects of the biogenesis and regulation of motile cilia function remain poorly understood, partly due to a lack of understanding of essential components that control these processes. Our studies on mammalian Hedgehog (Hh) signaling led to the unexpected finding that Fused (Fu), a putative serine-threonine kinase, and Kif27, a kinesin, are key players in regulating motile cilia function, independent of Hh signaling. Thus, studies on Fu and Kif27 provide new mouse models of human PCD. More importantly, they serve to bridge the gap in our understanding of the steps between transcription factors essential for ciliogenesis and construction and maintenance of the motile cilia. We propose the following specific aims: 1) Test the hypothesis that Fu interacts with central pair proteins to regulate their localization and assembly during motile cilia biogenesis. 2) Elucidate the functional interactions between Fu and Kif27 in controlling motile cilia function. 3) Define the role of Fu in controlling motile cilia orientation. 4) Identify Fu targets in controlling ciliogenesis through a combination of candidate gene approaches and systematic chemical labeling methods.